1. Field of the Invention
The present invention relates to an optical switch, and in particular to an optical switch that separates light according to a wavelength.
2. Description of the Related Art
In recent years, a technology for transmitting by multiplexing optical signals of different wavelengths in one optical fiber has been used practically. For example, a structure in which a plurality of signals that have been multiplexed are separated for each optical signal of different wavelength and then switched by using a mirror has been disclosed in Japanese Patent Application Laid-open Publication No. 2003-101479. In the structure disclosed in the Japanese Patent Application Laid-open Publication No. 2003-101479, to start with, light emitted from an input port, which is an optical fiber for input, is converted into parallel light by a micro lens array which is a collimating lens. The parallel light is reflected by a diffraction grating for spectrum. The light reflected passes through a second lens which is an image forming lens. By this, the light emitted from the input port is separated spatially for different wavelength. The light separated spatially is incident on different mirrors in a mirror array according to the wavelength. The mirror array includes a plurality of mirrors for which an angle of a reflecting surface can be controlled independently. The light incident on the mirror is reflected upon deflection according to an angle of the mirror. The reflected light again passes through the second lens and is incident on the diffraction grating. The light reflected by the diffraction grating is incident on an output port which is an optical fiber for output. The optical signal is output (switched) to a desired optical fiber for output by changing the angle of the mirror.
However, the angle of the mirror sometimes differs from a predetermined angle due to an effect of a change in an environment such as temperature and humidity, and a change due to an elapsed time. If the angle of the mirror differs from the predetermined angle, light emitted from the optical fiber for input cannot be allowed to be incident accurately on the desired optical fiber for output. In such case, it is not possible to ascertain whether the light from the optical fiber for input is output (switched) accurately on the optical fiber for output or not. For this reason there is an increase in a loss of the output signal. Moreover, if a part of light is incident on an optical fiber for output other than the desired optical fiber for output, there is a possibility of a cross talk.